1. Field
The present invention relates generally to communications systems, and more specifically, to antenna beam steering techniques in a wireless communications environment.
2. Background
Mobile radio systems allow users to travel freely within a designated service area and communicate with any wireless telephony device or personal communications systems. One such mobile radio system is a code division multiple access (CDMA) cellular system. The CDMA cellular system is a modulation and multiple access scheme based on spread-spectrum communications. In a CDMA cellular system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different pseudo-random binary sequence that modulates a carrier, and thereby, spreads the spectrum of the signal waveform. The transmitted signals are separated in the receiver by a correlator that uses a corresponding pseudo-random binary sequence to despread the desired signal's spectrum. The undesired signals, whose pseudo-random binary sequence do not match, are not despread in bandwidth and contribute only to noise.
One of the major parameters that determine the capacity of a CDMA cellular system is the ratio of the energy per bit to the noise power spectral density (Eb/No). Thus, the capacity of the CDMA cellular system can be increased if the noise can be decreased. Since the undesired signals applied to the correlator of the receiver contribute to noise, the capacity of the CDMA cellular system can be improved by effectively blocking the undesired signals by optimizing the beam pattern of the antenna. Besides improving the capacity of the CDMA cellular system, this optimized beam pattern may reduce the transmission power required to overcome noise and interference. This reduced power requirement can reduce the cost and allow lower power units to operate at greater ranges. Preferably, the optimization of beam pattern should not compromise the ability of the CDMA cellular system to process multi-path components or search for new communications channels. Accordingly, there is a need in the art for systems and techniques for controlling a beam pattern of an antenna to effectively block undesired signals while maintaining the ability to process multi-path components and search for new communications channels.